We can say without doubt that GIMP does the same and more than most design and retouch programs you pay for. And of course it`s totally free.
It has been compared, justifiably, with the excellent Photoshop, which says a lot about its qualities.
It supports multiple layers, it has a do/undo function almost without limits, you can open multiple images simultaneously, redimension images, rotate them, invert colours, mirror them, it has a geometric selection (circles, squares...), it has a gradient editor, and also supports JPG, GIF, PNG, TIF, BMP, PCX...formats
All this with its own tools that are based on Linux, and with more than 100 plug-ins. Really essential for any graphic designer to be proud of.